NAME¶
fcopy - Copy data from one channel to another.
SYNOPSIS¶
fcopy inchan outchan ?
-size size?
?
-command callback?
DESCRIPTION¶
The
fcopy command copies data from one I/O channel,
inchan to
another I/O channel,
outchan. The
fcopy command leverages the
buffering in the Tcl I/O system to avoid extra copies and to avoid buffering
too much data in main memory when copying large files to slow destinations
like network sockets.
The
fcopy command transfers data from
inchan until end of file or
size bytes have been transferred. If no
-size argument is given,
then the copy goes until end of file. All the data read from
inchan is
copied to
outchan. Without the
-command option,
fcopy
blocks until the copy is complete and returns the number of bytes written to
outchan.
The
-command argument makes
fcopy work in the background. In this
case it returns immediately and the
callback is invoked later when the
copy completes. The
callback is called with one or two additional
arguments that indicates how many bytes were written to
outchan. If an
error occurred during the background copy, the second argument is the error
string associated with the error. With a background copy, it is not necessary
to put
inchan or
outchan into non-blocking mode; the
fcopy command takes care of that automatically. However, it is
necessary to enter the event loop by using the
vwait command or by
using Tk.
You are not allowed to do other I/O operations with
inchan or
outchan during a background fcopy. If either
inchan or
outchan get closed while the copy is in progress, the current copy is
stopped and the command callback is
not made. If
inchan is
closed, then all data already queued for
outchan is written out.
Note that
inchan can become readable during a background copy. You should
turn off any
fileevent handlers during a background copy so those
handlers do not interfere with the copy. Any I/O attempted by a
fileevent handler will get a "channel busy" error.
Fcopy translates end-of-line sequences in
inchan and
outchan according to the
-translation option for these channels.
See the manual entry for
fconfigure for details on the
-translation option. The translations mean that the number of bytes
read from
inchan can be different than the number of bytes written to
outchan. Only the number of bytes written to
outchan is
reported, either as the return value of a synchronous
fcopy or as the
argument to the callback for an asynchronous
fcopy.
Fcopy obeys the encodings configured for the channels. This means that
the incoming characters are converted internally first UTF-8 and then into the
encoding of the channel
fcopy writes to. See the manual entry for
fconfigure for details on the
-encoding option. No conversion is
done if both channels are set to encoding "binary". If only the
output channel is set to encoding "binary" the system will write the
internal UTF-8 representation of the incoming characters. If only the input
channel is set to encoding "binary" the system will assume that the
incoming bytes are valid UTF-8 characters and convert them according to the
output encoding. The behaviour of the system for bytes which are not valid
UTF-8 characters is undefined in this case.
EXAMPLE¶
This first example shows how the callback gets passed the number of bytes
transferred. It also uses vwait to put the application into the event loop. Of
course, this simplified example could be done without the command callback.
proc Cleanup {in out bytes {error {}}} {
global total
set total $bytes
close $in
close $out
if {[string length $error] != 0} {
# error occurred during the copy
}
}
set in [open $file1]
set out [socket $server $port]
fcopy $in $out -command [list Cleanup $in $out]
vwait total
The second example copies in chunks and tests for end of file in the command
callback
proc CopyMore {in out chunk bytes {error {}}} {
global total done
incr total $bytes
if {([string length $error] != 0) || [eof $in]} {
set done $total
close $in
close $out
} else {
fcopy $in $out -command [list CopyMore $in $out $chunk] \
-size $chunk
}
}
set in [open $file1]
set out [socket $server $port]
set chunk 1024
set total 0
fcopy $in $out -command [list CopyMore $in $out $chunk] -size $chunk
vwait done
SEE ALSO¶
eof(3tcl), fblocked(3tcl), fconfigure(3tcl)
KEYWORDS¶
blocking, channel, end of line, end of file, nonblocking, read,
translation